Closed cycle engine



July 14, 1953 L- F- CAMPBELL 2,645,216

' CLOSED CYCLE: ENGINE Filed Jan. 21, 1945 I 2 sheets-sheet 1 EXHAUST :nom 2,3. 4

LAWRENCE F CAMPBELL CLOSED CYCLE ENGINE Filed Jan. 21, 19,43

JMDHL MILIUHL INVENTOR` LAWRENCE F. CAMPBELL v ga/J ,'Z ATTORNEY Patented July 14, 1953 UNITED. 'STATESvv PA'.IIiN'IV yOFFICE 2,645,216l H lCLOSED CYCLEENGINE v .e Lawrence' F. oampbeu, silver spring, Ma. AApplication;rarluary21,1943, serialfNo. 473,051l y* sentais." (o1. lese-iis) i (Granted under This invention relates to internal combustion engines, and it is particularly concerned with-the operation of such engines in the absence of the atmosphere or where the normally plentiful supply of atmospheric oxygen is not available.

Internal combustionY engines are used extensively for propulsion of alll kinds of vehicles-because they are capable of delivering high power, are comparatively eiiicient and their `fuel is easily carried. However, all 'such engines require oxygen for combustion of the fuel, and this/isv ordinarily obtained in unlimited quantity from the atmosphere. Diesell engines,- which are the most eflicient, require exceptionally large amounts of Aair because for this'type of enginev agreater excess ofY oxygen is required Iover lthat necessary to burn the fuel for stable,'dependable operation. Therefore, as a practical matten'internal combustion engines have been confined to uses Where air is plentiful, and for-services in the absence of air it has been generally necessary to employ electric power. y i

One of the most tuting a disproportionately largepartof thevessels displacement. Also,A whilev on. thevr surface, it is necessary for the diesel engine to operate a generator to recharge thestorage batteries. The.

advantages of dispensing with the present under'- water method of submarine propulsionby permitting operation of the internal combustionen-y gine at all times, such as the large savingin weight, space, power requirements and maintenence,are so obvious that many experimenters have attempted for years to solve the problem of opere ating an internal combustion engine-inthe ab-f sence of the atmosphere.

With respect to submarine propulsion the oper4 ation of an internal combustionv Iengine vunder water presents two problems not necessarily present in its operation merely in the absence of the atmosphere, and thesefare: (l) efficient use of the oxygen provided for combustion-of the fuel, and (2) disposal of exhaust in such a manner as willA not cause awake onl the surface of the Water:

Methods fordisposing of thejexhaust include (a) compressing and storing'it, (b) absorbing theV carbon dioxide in a scrubbing columnfandfstoring the "unabsorbed gases, and (3)"'dscharging striking ofk these situations isl the operation of a submarine. iWhilefon the sur' face of the sea the Ivessel is propelled by means of' Title 35, U; S. Code (1952), sec. 266k) the exhaust into the to give a line dispersion'. y

This invention provides a method of operating internal combustion engines, particularly diesell I engines, of, either the twoor four-stroke type, not

only inzthe'absence of the atmosphere, but also under water,"` vThe method includesoperation of the enginejwi'th high oxygen efficiency and with an exhaust which-can easily bedisposed of without creating telltale evidence, so that the method also includes underwater propulsion.A The inventionalso includes internal combustion engines, particularly diesel engines, especially designed for such operation and eminently suited for propulsion of submarines .both on the surface yof the sea and underwater. k

In the absence of the atmosphere it is necessary to supply oxygen to` theengin'ein the same way that the fuel is supplied, that is, from storage tanks or reservoirs maintained in thev vehicle.

Accordingly it has been proposed to carry highly compressedl or liquiiied air in suitable pressure' tanks inthe submarine for operation nof the engines. This proposal has proven to be impractical Y. for a number of reasons.

about 31/2 kand 4 poundsof oxygen are required- For one thing, between for combustion of eachpound 0f ordinarydiesel fueloiLiWhich requires ycompressing (or liquify ingitandstoring approximately 15 to 17' pounds of`air' foreach pound of fuel to be used under titles of nitrogen and waterfvapor, and diesel en gine exhaust also includes large quantities of carbon ,-dioxide, a. considerable amount of unused oxygen and a small amount of carbon monoxide.4 When such an exhaust. is disposed. of, .for exdifferent situation. Both of these gases are only 50T sparingly soluble in water with the result that they are, not removed by scrubbing and if discharged into the sea they rise to the surface and leave a noticeable trail or wake of themovements ofthe submarine.V This is true even at great where Vthe hydrostatic pressure is Very; high. Therefore, anhough air is a suitau" sea through: porous plates The carbon monoxide is.

medium for combustion, it is undesirable from the standpoint of underwater exhaust disposal because there is no way to get rid of the nitrogen in the exhaust.

Instead of using air, the method of this invention uses oxygen, preferably substantially free of nitrogen with which to burn the fuel in the engine. The oxygen may conveniently be stored under pressure or be liquefied. Such a system requires that the oxygen be used efficiently and that the concentration of the oxygen in the exhaust be below that which would hinder exhaust disposal as described above. In general it is highly advanf tageous to have the oxygen concentration below about oxygen on a dry basis (i. e. about 6% oxygen if the Water Vapor is taken into considere ation).

As is well known, it is impraeticalto operate an internal combustion engine on a mixture ofV pure oxygen and fuel because of the excessively high temperatures reached and the detonation of the mixture, rather than its` burning, in the cylinders. It is also known that internal combustion engines will not operate satisfactorily if the oxygen concentration is low, even though the amount of oxygen present in the cylinder may be enough for stoichiometric combustion of the fuel. This is particularly true of diesel engines. The presence of these limits requires (l) that an inert gas be present in the cylinders during firing, and (2) that some method be employed for reducing the oxygen concentration in the exhaust, and it should accomplish useful work at the same time.

The method of this invention meets the first requirement by recirculating the exhaust gases back into the cylinders, after suitable enrichment with oxygen, and bleeding off a small amount of the exhaust equivalent to the increase in carbon dioxide and water caused by combustion ofv the fuel.

Experience has shown that stable dependable operation of the engine is not compatible with maintenance of a minimum of oxygen in the exhaust, under ordinary methods of operation. Theoretically, the maximum amount of oxygen necessary in the cylinders is the stoichiometric amount for combustion of the fuel. However, it is exceedingly difficult to obtain complete combustion under this condition, and the operation is critical and unstable. with diesel engines, and it isimpossible to operate any two-stroke diesel engines on such proportions of fuel to oxygen because of the excess air (orv the secondary one supplied With the exhaust froml the first with addition of only suiiicient oxygen to permit ignition in the cylinders. This pro'- posal has proven little better in practice than operation of the single engine on reduced oxygen because the secondary engine is subject to the same erratic operation, andthe primaryI engine depends on the secondary one for removal of its exhaust.

The method of this invention obviates the diffi-v culties of erratic operation of the secondary engine as Well as of the primaryv one by main-j4 taining extremely close coupling between thetwo,

not only with respect to the delivery` o f power.

It is particularly true.

4 but also with respect to the transfer of exhaust from one to the other. The primary and secondary engines may have their shafts direct coupled or through gears, or by electrical means or other positive common transmission system, but the preferred form of the invention combines the primary and secondary engines into a single engine byfthe simple means of isolating one or more cylindersl from the main bank, and supplying the bleed-off exhaust from the main bank to these isolated cylinders (which may be referred to as "economizer cylinders) with only enough oxygen added to permit combustion. The main bank "is Voperatedwith excess oxygen. In this way the closest possible coupling is maintained in all respects between the primary or main bank which is operated under ideal combustion conditions and the one or more economizer cylinders, or secondary bank, cannot falter or stop because of impulsive disturbances, variations in load, and the like, with the result that the engine operates stably and dependably rand is' free from critical adjustment.

In order. that the invention maybe more clearly understood the operationl of. ia four-cylinder diesel engine is described in detail with reference to the accompanying drawings in which:

Fig. 1 is a diagrammatic showing ofthe invention applied to a four-cylinder diesel engine.

Fig. 2 illustrates, diagrammatically, Vthe use of two separate engines,l and` the coupling betvs'feen them. f

Referring to the4 drawings in detail and first to Fig. l, here is shown, symbolically, a diesel engine I0 with four cylinders numbered I to l;l for identi,-

fication. A branch II o f an intake manifold I2- supplies air or oxygen to cylinders 2, 3 and 4, anda branch I3 of the intake manifold I2y supplies cylinder IA (the economiser cylinder). An exhaust manifold I4, connectedto cylinders 2, 3` and 4, connects to a heat interchanger or cooler I5 which, in turn is connected to an outlet valve IE by means of a pipe I,`I,. lThe pipe I'I; also connects toa pipe I8 through a valve I9. Theppe I8 connects an inlet valve 20 and the valve I9, with the intake of a supercharger Or. compressor 2| (driven by the engine I0) Which discharges into the intake manifold I2.

Fuel is supplied. tov standard injection pumps at each cylinder through a line 22, controlled by a valve 23, inthe customary manner.

Oxygenis supplied through a line 24, controlled by a valve 25, which enters the branch I.| of the man'ifoldl I2justprior. tothe cylinders 2, 3 and 4, and enters the branch I3l just before the intake of cylinder. I. The` oxygen to. cylinder l is controlledY by a valve 26. This providesthe differ.- entialI oxygen control whereby cylinders 2, 3 and 4. are run on a plentiful supply and cylinder I is run ona restricted, supply, so. that the, nal exhaustdischarged from the engine contains very little unused, oxygen.

The exhaust from cylinder. I, is normally, removed through a pipe 'llvvhich` may be vented (for` surface` operation)l through. a valve 34. or discharged through a valve Sito a pump 2 8 (for underwatelzoperation) which may be driven by.

I tends to pull'a, vacuum intheintake manifold I'Zfwhenthe engine'ffislightlyloaded, and this is true in spite fof Ythe "compressori 2 I.'i Therefore a renewal-.9imminence2.1 fs provided' asia @aanbreken .Theerase.geeififvlinf acariensV I are prevented from by-passing. through the loop 29 by a fast-.acting Vballcheclrifvalve..3llig When the return loop 28 is not .used, it. may be closed olf by a valve 33; Alsoa surge chamber 3l is provided in the loop 29 on the intake side of the check valve 30.to reducefluctuationsof intake pressure. A;

For ordinary, open cycled-operation, :suchz'as would be employed for submarine propulsion on the surface of the sea, the valves I9, 25, 33 and are closed andthe valves IIL-:20 and 3.4 are open. The air is drawn in'through the valve120f and is distributedto all cylindersrthrough'the manifold l2. Similarly the exhaust of cylinders 2, 3l and 4 is dischargedv through thevalve I6 and the exhaust from cylinder; l is dischargedthroughv the line 21 and vented directly to the air. Fuel is supplied throughthe-linejz, and .the engineV operates in the usualmanner. i

For closed cycle operationthevalves. I9, 33-and 35 are openedand the valves I6', 20 and 34 are closed. At the Sametime oxygenfissuppliedgto the.` cylinders by opening thev valve ,25.1y In order.

dioxide in the intake. Therefore a small amountg of oxygen is vadded-to bringrthe4 concentration just high enough to rei-n the cylinder (forthis engine it was about 20%). Runs over long periods consistently showed an oxygen concen,

tration in the exhaust removedfrom cylinder- I of lower than 5% on a dry basisy (about 3% ona wet basis) which is negligible.. A certain amount of gas leakage around lthepistons 'is unavoidable. so that the crankcase soon builds up a slight posi-g tive pressure unless a breather opening isprovided. However, when under waterjtheseffumes.

must not escape into the submarine and,as they represent a fuel yand Oxygen vloss anyway, `.they are returned to the pipe I8 by meansof a. blower or pump 32 and valve 36.

der I and the other lcylindersshows thatv cylinder I consistently delivers usef'ulwork.V .Since the entire bleed-ofi exhaust from the other cylinders must pass through cylinder l` wherethe oxygenis.- reduced to a low concentration, an economyof. oxygen is obtained. Thus, the use of 'oneicylinder ofthe engine (which `is always synchronized with the other cylindersl as an economizer cylinder permits a highdegreejof Yoxygen efficiency and at the same time reduces the concentration in the exhaust to the point Where disposal thereof in any of the ways indicated above is easily effected.' -And all this is done'without Aail'e'cti'ng the dependability or smoothnessiof the engines operation. if li The supercharger 2| is not necessary to' the satisfactory operation of the engine in closed cycle operation because the amount of oxygen fed to the cylinders is at all times controllable. However, the supercharger reduces the back pressure on the primary bank of cylinders and thus also aids in the scavenging of exhaust gases.

The number of cylinders which must `be de voted to reducing the oxygen concentration in the exhaust, i. e., economzer,.cylinders, ..will

depend on the total number .of cylindersfinthe engine. At least one cylinder is required; and the ,smaller the number thatcan. be employed-.to removey the products of. combustion. under .full load the umoreeiiicient and dependable'will .:be.

the operation of the .engine Obviouslyit is notl necessaryto discharge allfof the exhaust from one or two economy cylinders. lIfdesired three, or fourA economy cylinders may be utilized in a, large engine (say where two would be adequate):,

recycling` a partA of their exhaust throughthe vacuum breaker loop and discharging therest,

if the most stableoperation is not required. Sim-v ilarly, less than the required number of economizer cylinders may be used,. if :optimum oxygen efficiency is not desired and part .of therecycled gases 1s removed from theengine withoutfpassing` through the economizer cylinders.4v #As an upper. limit itis inadvisable to employmorecthan half of the vcylinders as economy .cylindersxbecause the engine becomes'.A less dependablelin loperation Y and it becomesv increasingly 'difficulttof keep the- OXygen concentration down to a minimum inthe exhaust.

The amount gases which irs-necessary depends on af-number of A comparison of time-pressure curves of vcylinfactors, andsome of'this heat canb'e utilized `to provide a comfortableatmosphere for the Jcrewiof.`

the submarine, or it canlbereasily removedby..

heat exchange with the sea. :The temperature limits between which-the cooled, recycledgases. should be maintained are. not-critical.w` Due to the highheat capacityof carbon dioxide,v as cornpared to nitrogen, the intake gases must be hotter than when'using. air, or else. the. adiabatic. com.4

pression in the cylinders willnot raisethe temperature high enough toignite .the fuel in a diesel engine.- Thus vthe functiontof. the heat inter.

changer I5 is tovextr'act heat fromthe recycled'- to permitlsatis-f.

gases, butto leave suilicienty heat factory ignition. f. -In the engine tested the.intake.temperature wasfound tobe optimumatgabout 200 t0'250 Of course, the exhausttemperatureswillnrun little higherin closed.' cycle operation than. when...

the engine is operating on air, so that the; maxi.- mum=eficiency, yand hence power output, will. be slightly less.

. Although the invention hasibeendescribed; in. detail with reference tova` diesel engine, the

method is equally applicable-to all kinds of internal combustion enginesr where; oxygen economy is important.v Also,';.while1the description has been confined primarily to rvsubmarine propulsion the invention can be :applied to any` situation where an. internal combustion .engine is used under.L conditions `of insufficient Y- atmos-:z 'pheric oxygen, such as stratospheric flight. l Asc-"has already been stated, the .method ,of this;

invention ycan* be accomplished Aby .passing the bleed-off from the rrecycled gases through fthe cylinder or. cylindersof a separate secondary. engine :tightlypoupled to the primary engine.y .The 'latter modication. is. Vdiagrarnrnatically illustrated in Fig. .2 where the primary'group' of cylinders?, 3' and y4. constitute one engine andA the secondary cylinder l constitutes'v a .separate engine closely coupled to the first through a common shaft.v The various elements of Fig. 2 corresponding to `certain elements of Fig. 1 are designated by the same reference numerals primed.

The invention described herein vmay be manu# factured and used by or for the Government of the United States of America for governmental of cooling of the recrzyoledexhaustl 7,. purposes without the .payment of 'any royalties thereon or therefor. r

I claim:

1. Method of operating a multi-wunder interrnal combustion engine in the absence ofY suiicient atmosphere for combustion which comprises; supplying fuel to the cylinders of said engine, for combustion therein, removingy exhaust from. a part of the total number of cylinders. in an amount. equivalent to the products of combustion maintain just sufficient oxygen for combustion. in the intake to any cylinder any exhaust of' which is removed from the engine.

2. Method of operating a multi-cylinder internal combustion engine as claimed in claim 1 which additionally includes preventing -build-up. ofvacuum in said intakes. during operation under. light load by returning a portion of the unre-v cycled exhaust to said intakes through a check,

valve.

3. Method of operating a multi-cylinder. internal combustion engine which comprises, s upply-` ing fuel to all the cylinders of said engine for` combustion therein, removing exhaust from a part of the total number of cylinders in an amount equivalent to the products of combustion of said engine, recycling the remaining exhaust gases. from said engine back to said irst men.- tioned cylinders, adding oxygen to said gases so as to maintain in the intakes to those cylinders` whose exhaust is completely recycled a substantial excess over that necessary for combustion and to maintain just suiiicient oxygen for combustion in the intake to any cylinder any exhaustof which is removed from the engine, and disposing ofthe removed exhaust.

4. Method as claimed in claim 3 wherein said engine is a diesel engine, and wherein theblowby from the cylinders is removed from the crankcase of said engine and returned to the. recycled exhaust gases.

5. Method of operating a power plant com tioned cylinders, adding oxygen to said gases, so. as to maintain in the intakes to those cylinders whose exhaust is completely recycled a substan-A tial excess over that necessary for combustion andV to maintain just suilicient oxygen for' combustion in the intake to any cylinder any exhaust of which is removed from the engines, returning.. the blowebyfrom the cylinders to said recycled. exhaustgases, and compressing the removed ex-v haust to apressure in excess of the hydrostaticY escape,

pressure on the submarine and letting it into the water.

56. Methodv of operating a power plant comprised of closelycoupled multi-cylinder diesel engines in a submerged submarine which comprises, supplying fuel to all the cylinders of said engines for combustion therein, removing exhaust from a` part-of the total number of cylinders in an amount equivalent to the products of combustion ofv said engines, recycling the remaining exhaust gases from said engines back to said rst mentioned-cylinders through a supercharger, adding oxygen to said gases so as to maintain in the intakes to those cylinders whose exhaust is completely recycled a substantial excess over` that necessary for combustion and to maintain just suicient oxygen for combustion in the intake to any--cylinderany exhaust'of which is removed from the engines, returning the blow-by from the cylinders tosaid recycled exhaust gases, and compressing the removed exhaust to a pressure in excess of the hydrostatic pressure on the submarine and letting it escape into the water.

"[An 4internal combustion engine capable of operating in the absence of the atmospherewhich comprises, a crankshaft, a plurality of cylinders and pistons connected to said crankshaft, means for .supplying fuel to said cylinders, an exhaust manifold connected to the largerpart of the total number of said cylinders, an intake manifold connected to all of said cylinders and to said exhaustfmanifold whereby exhaust gases are recycledvba'ck to said cylinders, means for supplying-oxygen to said gases so that a substantial excessof oxygen is supplied to the intakes to those cylinders connected to said exhaust manifold and only suilicient oxygen for combustion is supplied to all other cylinders, and means for removing exhaust from said other cylinders equivalent'to the products of combustion of the entire engine. I

8.V Method of operating a power plant comprised of a plurality of internal combustion engine cylinders in the absence of suiicient atmos' 1 bustion andgto maintain just suiiicient oxygen for combustion in the intake to said secondary group.

LAWRENCE F. CAMPBELL.

vReferencesv Cited in the le of this patent .EUNITED STATES PATENTS Number Name Date 1,099,445 Jaubert June 9, 1914 1,950,586 ,ZubatyY Mar. 13, 1934 2,113,601 Pratt Apr. 12, 1938 WydlerA July 22, 1941 

